Salad dressings are generally high in calories and preservatives. They aren't overly cheap, and they tend to go bad after a few months. Avoid buying salad dressing and instead invest in some good quality extra virgin olive oil and balsamic vinegar. Pour a little of each over your salad right before you eat it. It gives the salad extra flavor, is much healthier, and is inexpensive. These two ingredients can also be used in other cooking and they both have long shelf lives.